In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive or a photoconductive member with subsequent rendering of the latent image visible by the application of particulate thermoplastic material, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or the photoconductor member, or transferred from either member to another support, such as a sheet of plain paper, with subsequent affixing by, for example, the application of heat and pressure of the image thereto.
To affix or fuse toner material onto a support member like paper by heat and pressure, it is usually necessary to elevate the temperature of the toner and simultaneously apply pressure sufficient to cause the constituents of the toner to become tacky and coalesce. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is known.
One approach to the heat and pressure fusing of toner images onto a support has been to pass the support with the toner images thereon between a pair of pressure engaged roller members, at least one of which is internally heated. For example, the support may pass between a fuser roller and a pressure roller. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rollers with the toner image contacting the fuser roll thereby to effect heating of the toner images within the nip.
The process of transferring charged toner particles from an image bearing member marking device, such as a photoconductor, to an image support substrate like a sheet of paper involves overcoming cohesive forces holding the toner particles to the image bearing member. The interface between the photoconductor surface and image support substrate may not in many instances be optimal or may be inconsistent, thus, in the transfer process when spaces or gaps exist between the developed image and the image support substrate the quality of the image may not be acceptable. One aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the cohesive forces acting on the toner particles as they rest on the photoconductive member. Careful and somewhat costly control of the electrostatic fields and other forces present can be required to induce the physical detachment and transfer of the charged toner particles without scattering or smearing of the developer material.
In general, transfer of developed toner images in electrostatographic applications has been accomplished via electrostatic induction using a corona generating device, wherein the image support substrate is placed in direct contact with the developed toner image on the photoconductive surface while the reverse side of the image support substrate is exposed to a corona discharge. This corona discharge generates ions having a polarity opposite that of the toner particles, thereby electrostatically attracting and transferring the toner particles from the photoreceptive member to the image support substrate.
More specifically, in the xerographic electrostatic transfer of the toner powder image to the copy sheet, it is necessary for the copy sheet to be in uniform intimate contact with the toner powder image developed on the photoconductive surface. In particular, non-flat or uneven image support substrates, such as copy sheets that have been mishandled, left exposed to the environment or previously passed through a fixing operation, such as heat and/or pressure fusing, tend to promulgate imperfect contact with the surface of the photoconductor. Further, in the event the copy sheet is wrinkled, the sheet will usually not be in intimate contact with the photoconductive surface and spaces, or air gaps, as illustrated herein, will materialize between the developed image on the photoconductive surface and the copy sheet. When spaces or gaps exist between the developed image and the copy substrate, there is a tendency for toner not to transfer across these gaps causing variable transfer efficiencies, and where areas of low or no transfer results in a phenomenon known as image transfer deletion.
Image transfer deletion is undesirable in that portions of the desired image may not be appropriately reproduced on the print sheet in that the area of the cleaning blade that contacts the photoreceptor and the cleaning blade will in most instances pick up residual dirt and toner from the photoreceptor surface. Therefore, in the next printing cycle the printed sheets with developed images thereon, the residual dirt present on the transfer assist blade is transferred to the back side of the print sheets resulting in unacceptable print quality defects.
The use of a known transfer assist blade incorporates melamine formaldehyde resins, where the formaldehyde, which can be emitted during curing, has been classified by the United States Environmental Protection Agency (EPA) as a known human carcinogen, and where the EPA has positioned formaldehyde with similar risk values as other human carcinogens such as benzene, butadiene, and vinyl chloride.
With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and redeveloping, all followed by transfer to paper, can be completed in a single revolution of the photoreceptor in so-called single pass machines, while multipass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color.
Mechanical devices, such as rollers, have been used to force the image support substrate into intimate and substantially uniform contact with the image bearing surface. For example, there can be selected an electrically biased transfer roll system in an attempt to minimize image deletions. In other electrophotographic printing machines, such as the color producing Xerox Corporation 1065 machine, the copy sheet is provided with a precisely controlled curvature as it enters the transfer station for providing enhanced contact pressure.
In single pass color machines, it is desirable to cause as little disturbance to the photoreceptor as possible so that motion errors are not propagated along the belt to cause image quality and color separation registration problems. One area that has potential to cause such a disturbance is when a sheet is released from the guide after having been brought into contact with the photoreceptor for transfer of the developed image thereto. This disturbance, which is often referred to as trail edge flip, can cause image defects on the sheet due to the motion of the sheet during transfer caused by energy released due to the bending forces of the sheet. Particularly in copying and printing machines which handle a large range of paper weights and sizes, it is difficult to have a sheet guide which can properly position any weight and size sheet while not causing the sheet to oscillate after having come in contact with the photoreceptor.
There is a need for members and processes that substantially avoid or minimize the disadvantages illustrated herein.
Also, there is a need for transfer assist members that are wear resistant and that can be used for extended time periods without being replaced.
Further, there is a need for transfer assist members that are environmentally acceptable and that are formaldehyde free.
There is also a need for toner developed image transfer assist members that permit the continuous contact between a photoconductor and the substrate to which the developed toner image is to be transferred, and an apparatus for enhancing contact between a copy sheet and a developed image positioned on a photoconductive member.
Yet another need resides in providing xerographic printing systems, inclusive of multi-color generating systems, where there is selected a transfer assist member that maintains sufficient constant pressure on the substrate to which a developed image is to be transferred and to substantially eliminate air gaps between the substrate and the photoconductor in that the presence of air gaps can cause air breakdown in the transfer field.
Further, there is a need for transfer assist members that enable suitable and full contact of the developed toner image present on a photoconductor and a substrate to which the developed image is to be transferred.
Additionally, there is a need for transfer assist members that contain durable formaldehyde free compositions that can be economically and efficiently manufactured, and where the amount of energy consumed is reduced.
Yet additionally there is a need for a multilayered transfer assist member that includes as one layer a check film on the side exposed to a dicorotron/corona, and which member possesses excellent resistance characteristics.
Also, there is a need for transfer assist members where the check film layer thereof can be generated by economical extrusion processing.
Further, there is a need for transfer assist members with a combination of excellent durability that exert sufficient constant pressure on a substrate sheet and permit the substrate to fully contact the toner developed image on a photoconductor, which members provide mechanical pressure, about 20 percent of its function and electrostatic pressure/tailoring about 80 percent of its function, and where complete transfer to a sheet of a toner developed image from a photoconductor results, such as for example, about 90 to about 100 percent, from about 90 to about 98 percent, from about 95 to about 99 percent, and in embodiments about 100 percent of the toner developed image is transferred to the sheet or a substrate, and wherein blurred final images are minimized or avoided.
Moreover, there is a need for composite transfer assist blades that overcome or minimize the problems associated with a single component blade, as a single component blade in order to be flexible enough to prevent image damage does not provide enough contact force to the back of the sheet to enable complete image transfer giving rise to transfer deletions and color shift.
Yet, there is another need for transfer assist members that include check films, and which members are useful in electrophotographic imaging apparatuses, including digital printing where the latent image is produced by a modulated laser beam, or ionographic printing, and where charges are deposited on a charge retentive surface in response to electronically generated or stored images.
Additionally, there is a need for a xerographic system containing an improved transfer assist blade (TAB) which is used in conjunction with a corona device to perform transfer, such as by effectively moving toner from a photoconductor media, and where the TAB functions to provide mechanical pressure and electrostatic pressure/tailoring, with the electrostatic pressure/tailoring being achieved by utilizing a check film comprising the disclosed crosslinked layer mixture on a supporting substrate.
These and other needs are achievable in embodiments with the transfer assist members and components thereof disclosed herein.